This invention relates to absorbing arrangements and methods for temporarily storing oxides of nitrogen and sulfur and removing such oxides from the exhaust gas from internal combustion engines.
As used herein, the term "absorb" includes the chemical process for storing gases such as, for example, by conversion of barium oxide to barium nitrate for storage of nitrogen oxide.
U.S. Pat. No. 4,755,499 discloses an arrangement for the reversible storage of oxides of nitrogen and sulfur, for example from motor vehicle exhaust gases, in which the absorber is regenerated by heating in a reducing atmosphere. In this arrangement, a reduction of the nitrogen oxides takes place at the same time.
A storage catalyst of that type for use in motor vehicles is described in more detail in U.S. Pat. No. 5,402,641, in which high temperatures above 500.degree. C. are necessary to regenerate the absorber. Consequently, use of the storage catalyst is possible only for motor vehicles having a high exhaust-gas temperature, in particular for motor vehicles with an Otto engine.
In this case, however, the possibility of use is limited since, under certain operating conditions of internal combustion engines, such as occur for example in city traffic, the acceleration phases cause a large emission of nitrogen oxide, but no long-lasting high temperature condition such as is required to regenerate the absorber, especially with respect to oxides of sulfur, is attained.